The invention relates to a photoacoustic sensor, comprising a resonance body which at least partly delimits a volume intended to hold molecules to be detected and an apparatus for identifying a vibration of the resonance body.
A. A. Kosterev et al.: Quartz-enhanced photoacoustic spectroscopy, Optics Letters, Vol. 27, No. 21 (2002) 1902 has disclosed a device of the type mentioned at the outset. This known detection method discloses the use of a fork-shaped quartz crystal as a highly sensitive microphone, by means of which pressure variations in a gas phase can be detected. According to the known method, the pressure variations are generated by means of a laser diode, which selectively excites the molecules in the gas phase by means of spectrally narrow-band radiation. The sensitivity of the photoacoustic measurements can be increased due to the high Q-factor of the fork-shaped quartz crystal used for the detection.
However, the method known from the prior art is disadvantageous in that the material selection for producing the fork-shaped element is restricted to piezoelectric materials. Hence, the signal processing requires the measurement of a signal voltage lying between a few picovolts and a few nanovolts. Measuring such small voltages is susceptible to electric disturbance signals. Furthermore, the known photoacoustic gas sensor cannot be used in explosive gas atmospheres because the piezoelectric sensor can cause an explosion by voltage sparkovers. Finally, the known measurement method cannot be used in hot gas atmospheres either because the piezoelectric materials used fail if the temperature is too high.
Proceeding from this prior art, the invention is therefore based on the object of specifying a method for gas analysis, which can be applied universally, even at high temperatures and in potentially explosive regions. Furthermore, the method should have increased reliability with respect to electric disturbance signals.